The present invention relates to substrates such as those used in inkjet printheads and the like. In particular, a substrate is coated with at least one thin film layer, and a slot region extends through the substrate and the thin film layer.
Various inkjet printing arrangements are known in the art and include both thermally actuated printheads and mechanically actuated printheads. Thermal actuated printheads tend to use resistive elements or the like to achieve ink expulsion, while mechanically actuated printheads tend to use piezoelectric transducers or the like.
A representative thermal inkjet printhead has a plurality of thin film resistors provided on a semiconductor substrate. A nozzle plate and a barrier layer are provided on the substrate and define the firing chambers about each of the resistors. Propagation of a current or a xe2x80x9cfire signalxe2x80x9d through a resistor causes ink in the corresponding firing chamber to be heated and expelled through the corresponding nozzle.
Ink is typically delivered to the firing chamber through a feed slot that is machined in the semiconductor substrate. The substrate usually has a rectangular shape, with the slot disposed longitudinally therein. Resistors are typically arranged in rows located on both sides of the slot and are preferably spaced approximately equal distances from the slot so that the ink channel length at each resistor is approximately equal. The width of the print swath achieved by one pass of a printhead is approximately equal to the length of the resistor rows, which in turn is approximately equal to the length of the slot.
Feed slots have typically been formed by sand drilling (also known as xe2x80x9csand slottingxe2x80x9d). This method is a rapid, relatively simple and scalable process. The sand blasting method is capable of forming an opening in a substrate with a high degree of accuracy, while generally avoiding substantial damage to surrounding components and materials. Also, it is capable of cutting openings in many different types of substrates without the generation of excessive heat. Furthermore, it allows for improved relative placement accuracies during the production process.
While sand slotting affords these apparent benefits, sand slotting is also disadvantageous in that it may cause microcracks in the semiconductor substrate that significantly reduce the substrates fracture strength, resulting in significant yield loss due to cracked die. Low fracture strength also limits substrate length which in turn adversely impacts print swath height and overall print speed.
In addition, sand slotting typically causes chips to the substrate on both the input and output side of the slot. This chipping causes two separate issues. Normally the chipping is tens of microns large and limits how close the firing chamber can be placed to the edge of the slot. Occasionally the chipping is larger and causes yield loss in the manufacturing process. The chipping problem is more prevalent as the desired slot length increases and the desired slot width decreases.
In the present invention, a coated substrate for a center feed printhead has a substrate, a thin film applied over the substrate, and a slot region extending through the substrate and the thin film. In one embodiment, a plurality of thin films, or a thin film stack, is deposited over the substrate. In this embodiment, the slot region extends through the plurality of thin films.
A slot is formed through the slot region of the substrate and the thin film(s). The thin film(s) applied over the substrate minimizes chip count in a shelf surrounding the slot and crack formation through the substrate. In one embodiment, the slot is formed mechanically.
In one embodiment, the thin film is at least one of a metal film, a polymer film, and a dielectric film. In another embodiment, the thin film material is ductile and/or deposited under compression.
In one embodiment, the substrate is silicon, and the thin film is an insulating layer grown from the substrate, such as field oxide. In one embodiment, the thin film is PSG. In one embodiment, the thin film is a passivation layer, such as at least one of silicon nitride and silicon carbide. In one embodiment, the thin film is a cavitation barrier layer, such as tantalum. In the present invention, any combination of thin films may be applied over the substrate.
The minimum thickness for each thin film layer is about 0.25 microns. In an embodiment where there are a plurality of thin films coated over the substrate, the thickness of the thin films is up to about 50 microns, depending upon the individual material and thickness of the layers applied. In one embodiment, the thickness of the thin film stack is at least about 2.5 microns.